1. Field of the Invention
This invention relates to extension ladders and particularly to those having leveler means that enable the ladders to be positioned upright or uneven or inclined surfaces.
2. Description of the Prior Art
Extension ladders that have a top section which slides relative to a bottom section for height adjustment are well known. Early ladders of this type were generally made of wood and the sections were held together by collar or angle iron units. More recently, extension ladders have been formed of metal, e.g., extruded aluminum or magnesium, and have siderails made with channel sections that provide interlocking engagement between the top and bottom ladder sections. Such interlock arrangement usually extends the entire length of the ladder and imposes limitations on attachments or appendages that may be applied to such ladders.
Extension ladders must frequently be used at locations that do not provide a level surface for support of the ladder. Hence, leveler means to permit upright positioning of the ladder on unlevel support surfaces have been developed. Such levelers have included slotted foot units (see U.S. Pat. No. 1,491,642), pin adjustable, slideable sleeves (see U.S. Pat. No. 809,057), cam-locking channel members (see U.S. Pat. No. 1,718,891) and pin adjustable channel extenders (see U.S. Pat. No. 1,246,709). Such prior known levelers, however, are not suitable for use with extruded metal ladders of the section interlocking type because they prevent free sliding of the top and bottom ladder sections.
Some forms of levelers have been applied to the interlocked-type metal ladders, but there exists a need for leveler means for this type of ladder that may be produced at low cost, will be fault-free and provide secure operation meeting OSHA requirements and do not interfer with the free sliding of the sections of the extension ladder.